But on Thursday, White House Press Secretary Jay Carney emphasized that nothing has changed in President Barack Obama's promised 2014 withdrawal from the 10-year war, NBC News reported.

"What Panetta said is that it could happen, that the transition to an Afghan security lead could be moved up to 2013, but he was not making an announcement about a decision that had been made," Carney said, NBC News reported. Panetta was just talking about discussions in Brussels, Carney said.

Still, U.S. military leaders joined NATO's top official and France in Brussels on Thursday in calling for Afghan forces to take the lead in all combat operations by mid-2013, The Associated Press reported.

French President Nicolas Sarkozy has also suggested in recent days that the coalition should gradually transition out of combat in 2013.

In 2010, NATO leaders agreed that Afghan forces would take control province by province until they have full responsibility for security in all of Afghanistan by the end of 2014. Until now, it was widely assumed that coalition troops would retain the lead role in military operations until that final handover.

But under the arrangement being discussed by NATO defense ministers in Brussels this week, coalition troops would no longer lead combat missions after mid- to late-2013, although they would still provide assistance to the Afghans.

Although some officials insisted publicly that the allies were united in the transition goals, a senior NATO official told The Associated Press that there is some disagreement about the newly suggested timeframe.

The official, who spoke on condition of anonymity in order to discuss closed-door discussions, said the expectation is that no final decision on the timing is expected before the NATO summit in Chicago in May.

Speaking to reporters before the two-day meeting in Brussels, NATO Secretary-General Anders Fogh Rasmussen said Afghanistan remains the alliance's top operational priority, and that the coalition has been making progress in the war.